Mechanics assumptions Flashcards
What assumptions are there for a particle?
mass is concentrated at a sing point
rotational forces and air resistance can be ignored
What assumptions are there for a rod?
mass is concentrated along a line
no thickness
rigid (doesn’t bend or buckle)
What assumptions are there for a lamina?
mass is distributed across a flat surface
What assumptions are there for a uniform body?
mass in concentrated at a single point at the geometric centre of the body (centre of mass)
What assumptions are there for a light object?
treats object as having zero mass
tension is the same at both ends of a light string
What assumptions are there for an inextensible string?
acceleration is the same in objects connected by a taut inextensible string
What assumptions are there for a smooth surface?
no friction between the surface and any object on it
What assumptions are there for a rough surface?
objects in contact with surface experience a frictional force if they are moving or acted on by a force
What assumptions are there for a wire?
treated as one dimensional
What assumptions are there for a smooth and light pulley?
pulley has no mass
tension is the same on either side of the pulley
What assumptions are there for a bead?
moves freely along a wire
tension is the same on either side of the bead
What assumptions are there for a peg?
dimensionless and fixed
can be rough or smooth depending on question
What assumptions are there for a air resistance?
usually modelled as negligible
What assumptions are there for a gravity?
all objects with mass are attracted towards the earth
earths gravity is uniform and acts down vertically
g is constant and is 9.8 ms^-2, unless stated otherwise
